This invention relates to restoral of data transmission between modems by switching transmission from a degraded line to a functioning line.
Modems often transmit data over leased lines, particularly when transmission is at high bit rates. When such lines fail or degrade, it is known to provide an alarm indication, and to provide the operator with a means for manually switching transmission, temporarily, from the leased line to a dial line (i.e., a Public Switched Telephone Network, or PSTN, line). Some modems have had the capability of automatically switching to a dial line upon loss of the data carrier on the leased lines.